1. Field of the Invention
This invention relates to a wrist AM radio receiver housed in a bracelet-like structure which is adapted to be removably wrapped about a user's wrist.
2. Description of the Prior Art
In existing AM radio receivers of the type to be worn on a user's wrist, a bar antenna, a speaker, a printed circuit board carrying circuit components, and all other elements of the radio receiver are arranged in a single block or assembly in an attempt to reduce the extent of the radio receiver and permit its being housed in a casing somewhat like that of a wristwatch. However, such arrangement of all of the elements of the AM radio receiver in a single block or assembly causes the same to have an undesirably large thickness, and further results in the bar antenna being relatively strongly influenced by emanations from other circuit components, thus causing noisy reception. The foregoing problem is particularly encountered in radio receivers using a phase-locked loop (PLL) synthesizer for generating the desired local oscillation or in wrist-type radio receivers having an electronic watch combined therewith, in each of which an oscillating elements acts as a reference oscillation source generating reference pulses or frequency-divided pulses to which the bar antenna is sensitive so that electrostatic noise is produced.
Therefore, it has not been considered feasible, in the case of AM radio receivers using a PLL synthesizer or combined with an electronic clock, to reduce the size thereof sufficiently for a wrist radio receiver. Of course, if an AM radio receiver using a PLL synthesizer or combined with an electronic watch is reduced in size so as to be capable of use as a wrist radio receiver, the susceptibility of the bar antenna to the reference pulses or other sources of noise among the receiver components may be substantially reduced by fully shielding all of the components of the receiver from each other. However, for such complete shielding of the receiver components, it may be necessary to employ plural metal layers in the shielding or to use special shielding metals, thereby undesirably increasing the complexity of the assembly and the time and labor required therefor. Further, the metallic layers or plates required for effective shielding will undesirably increase the cost of the materials for the radio receiver and will substantially impair the sensitivity of the reception by the radio receiver.